Active pushbroom imaging system using a micro-electro-mechanical system (mems) micro-mirror array (mma)

ABSTRACT

An active imaging system uses a MEMS Micro-Mirror Array to form and scan an optical beam over a first portion of scene within a first edge region of the field-of-view of the optical receiver in the direction of motion of the imaging system. In addition to tip and tilt control of the mirrors, the MMA may have piston control which can be used to minimize diffraction losses when focusing and scanning the beam, provide wavefront correction or to compensate for path length variations. The MMA may be partitioned into segments to independently form and scan a plurality of optical beams, which may be used to scan the first or different portions of the scene. The different segments may be provided with reflective coatings at different wavelengths to provide for multi-spectral imaging. The different segments may be used to combine multiple optical sources to increase power or provide multi-spectral illumination.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to active imaging systems, and more particularlyto systems that scan a laser beam to illuminate selected portions of ascene.

Description of the Related Art

Typical active imaging systems use laser radiation to image a scene. Thescene is imaged by sensing reflections of the laser radiation at adetector, which can often include a Focal Plane Array (FPA). FPAsgenerally include an array of pixels organized in rows and columns. Acircuit associated with each pixel of the FPA accumulates chargecorresponding to the flux of incident radiation at the correspondingpixel. Typically, the charge within the pixel is accumulated at acapacitive element, which produces a voltage proportional to theaccumulated charge. The resulting voltage is conveyed by additionalcircuitry to an output of the FPA, and may be used to generate an imageof the scene.

The ability of an imaging system to accurately convert optical energy todigital information is generally dependent on the sensitivity of thedetector, and the intensity of the illumination emitted by the opticalsource. For example, in various conventional imaging approaches, theoptical source is positioned to continuously illuminate the entire scenewithin a field-of-view of a receiver. Such an approach can consume agreat deal of power when continuously providing the intensity ofillumination necessary for high-contrast imaging across the entirescene. Alternative approaches to imaging utilize mechanical beamsteeringoptics, such as gimbal-based systems. Gimbals allow the physicaldisplacement (e.g., rotation) of the system to reduce power consumptionand enable selective aiming. However, these alternative approaches toimaging are, in general, limited by the capability of the mechanicalelements. Limitations may include, but are not limited to, the speed ofthe executed scan and the pattern illumination. Moreover, thesemechanical assemblies can be complex, and may increase the weight andcost of the imaging system and associated elements, such as motioncompensating elements.

U.S. Pat. No. 10,321,037 entitled “Active Pushbroom Scanning System andMethod” issued Jun. 11, 2019 discloses an active imaging system thatincludes a non-mechanical beamsteering device such as a liquid crystalwaveguide (LCWG), which directs illumination over a desired extent of ascene based on a detected direction of motion of the imaging system.Although the LCWG is capable of rapid steering, the LCWG can only steera very narrow band of wavelengths about a center wavelength. Furthermoreeach material system e.g., substrates, coatings and liquid crystals, andvoltage settings to steer the laser beam are unique to each centerwavelength. Therefore to accommodate different wavelengths requiresdifferent LCWG devices and significant investment in materials,manufacturing, set-up and calibration etc. to design and field eachdevice. The imaging system may image a leading edge of a field-of-viewof an optical receiver, or may track one or more varying features withinthe field-of-view, based on the detected direction of motion. Theimaging system is configured to perform rapid imaging scans based on themovement of the imaging system (or variations in motion of a featurewithin a scene) while maintaining a reduced weight, size, and powerconsumption for ground, mobile, maritime, airborne, and space imagingenvironments.

SUMMARY OF THE INVENTION

The following is a summary of the invention in order to provide a basicunderstanding of some aspects of the invention. This summary is notintended to identify key or critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts of the invention in a simplified form as a prelude to themore detailed description and the defining claims that are presentedlater.

Aspects and embodiments are generally directed to active imaging systemsand methods, and, in particular, to active imaging systems and methodswhich include a Micro-Electro-Mechanical System (MEMS) Micro-mirrorArray (MMA) for active scanning applications. In certain examples, theactive imaging system includes a MEMS MMA with tip, tilt and pistonmirror actuation which directs and focuses illumination over a desiredextent of a scene based on a detected direction of motion of the imagingsystem. Specifically, the system may image a leading edge of afield-of-view (FOV) of an optical receiver, or may track one or morevarying features within the FOV, based on the detected direction ofmotion. Accordingly, various aspects and embodiments provide an imagingsystem configured to perform rapid imaging scans based on the movementof the imaging system (or variations in motion of a feature within ascene) while maintaining a reduced weight, size, and power consumptionfor ground, mobile, maritime, airborne, and space imaging environments.

According to an aspect, provided is an active imaging system. In oneexample, the active imaging system comprises a positioning systemconfigured to detect a direction of motion of the imaging systemrelative to a scene to be imaged, an optical source positioned to emitelectromagnetic radiation along a transmit path, a MEMS MMA positionedalong the transmit path to receive the electromagnetic radiation fromthe optical source and configured to form and scan the electromagneticradiation in an optical beam over at least a first portion of the scenewithin a FOV of an optical receiver, and the optical receiver positionedto receive reflections of the electromagnetic radiation from at leastthe first portion of the scene within the FOV, and the first portion ofthe scene is within a first edge region of the FOV of the opticalreceiver, the first (or leading) edge region being perpendicular to thedirection of motion of the imaging system to illuminate a new portion ofthe scene.

In different embodiments, the MEMS MMA may use the piston actuation ofthe micro-mirrors in combination with tip and tilt to approximate acontinuous reflective mirror surface to focus and scan the optical beam.This reduces diffraction from the edges of the mirrors therebyincreasing optical power in the focused spot. Piston actuation may alsobe used to provide wavefront correction for the focused optical beam tocompensate for atmospheric fluctuations or to compensate for path lengthvariation of the focused optical beam through the window of the imagingsystem. This piston actuation appears as deviations from the continuousmirror surface.

In different embodiments, the MEMS MMA may be partitioned into aplurality of segments, each segment comprising a plurality of mirrorsresponsive to command signals to tip and tilt, and possibly translate,the mirrors to form the electromagnetic radiation into an optical beam.The MEMS MMA may be configured to scan the plurality of optical beams inparallel over different sub-portions of the first portion of the scene.The MEMS MMA may be partitioned into a sufficient number of segmentssuch that each segment produces a fixed optical beam to instantlyilluminate the entire first portion of the scene. Alternately, the MEMSMMA may be configured so that at least one optical beam is scanned overthe first portion of the scene and at least one optical beam is scannedto revisit a previously scanned portion of the scene.

In an embodiment, the optical source emits electromagnetic radiationover a broadband that includes multiple discrete wavelengths. Themicro-mirrors are provided with a reflective coating that reflects overa band that includes the multiple discrete wavelengths, whereby theoptical beam comprises the multiple discrete wavelengths to scan thefirst portion of the scene.

In an embodiment, the MEMS MMA is partitioned into sections eachcomprising a plurality of mirrors. The mirrors in the different sectionsare provided with reflective coatings designed to reflect at differentwavelengths within a specified band. Within each section, themicro-mirrors are responsive to command signals to tip and tilt, andpossibly translate, the mirrors to form the electromagnetic radiationinto an optical beam at the wavelength corresponding to that section.One or more sections of the MEMS MMA may be segmented to produce aplurality of independently scanned optical beams at the correspondingwavelength. The MEMS MMA may scan the optical beams at the differentwavelengths over the first portion to provide multi-spectralillumination of the first portion. Alternately, the MEMS MMA may scanthe plurality of focused optical beams over the first portion and adifferent portion of the scene.

In an embodiment, the MEMS MMA is partitioned into sections eachcomprising a plurality of mirrors. A plurality of optical sources arepositioned to emit electromagnetic radiation along different transmitpaths, each path illuminating a different section of the MEMS MMA. Eachsaid section is configured to form and scan the electromagneticradiation in an optical beam and to combine the plurality of focusedoptical beams into a combined focused optical beam. In the case wherethe optical sources all emit at the same wavelength the combined focusedoptical beam behaves as if it were emitted from a single aperture laser,but with higher power than can be obtained from a single laser aperture.In the case where the optical sources emit at different wavelengths, thecombined focused optical beam is multi-spectral.

These and other features and advantages of the invention will beapparent to those skilled in the art from the following detaileddescription of preferred embodiments, taken together with theaccompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below withreference to the accompanying figures, which are not intended to bedrawn to scale. The figures are included to provide illustration and afurther understanding of the various aspects and embodiments, and areincorporated in and constitute a part of this specification, but are notintended as a definition of the limits of the invention. In the figures,each identical or nearly identical component that is illustrated invarious figures is represented by a like numeral. For purposes ofclarity, not every component may be labeled in every figure. In thefigures:

FIG. 1 is a block diagram of an example active imaging system in which aMEMS MMA is used to form and scan an optical beam according to aspectsof the invention;

FIGS. 2A and 2B are illustrations of an embodiment of a Tip/Tilt/Piston(“TTP”) MEMS MMA and a single mirror actuated to tip, tilt and translate(piston);

FIG. 3 is an example illustration of electromagnetic radiation receivedat the optical receiver of the active imaging system illustrated in FIG.1, according to aspects of the invention;

FIG. 4 is another example illustration of electromagnetic radiationreceived at the optical receiver of the active imaging systemillustrated in FIG. 1, according to aspects of the invention;

FIG. 5 is another example illustration of electromagnetic radiationreceived at the optical receiver of the active imaging systemillustrated in FIG. 1, according to aspects of the invention;

FIG. 6 is an illustration of tip and tilt mirror actuation to scan theoptical beam;

FIGS. 7A and 7B are side and top views of tip and tilt actuation to forma reflective lens to focus the optical beam into a spot;

FIG. 8 is an illustration of tip and tilt mirror actuation to focus andscan the optical beam;

FIG. 9 is an illustration of using tip, tilt and piston mirror actuationto approximate a continuous optical surface to focus and steer anoptical beam;

FIG. 10 is an illustration of using piston mirror actuation to producedeviations from the continuous optical surface to compensate for pathlength variations and/or to provide wavefront correction for opticaldistortion;

FIGS. 11A-11D are illustrations of an embodiment in which the MEMS MMAis partitioned into a plurality of segments each comprising a pluralityof mirrors that focus and independently scan an optical beam over thefirst portion of the scene in parallel or instantly or over the firstportion of the scene and to revisit previously scanned portions of thescene;

FIGS. 12A-12B are illustrations of an embodiment in which the MEMS MMAis partitioned into a plurality of sections each comprising a pluralityof mirrors that are provided with reflective coatings at differentwavelengths to focus and independently scan focused optical beams atdifferent wavelengths; and

FIG. 13 is an illustration of an embodiment in which the MEMS MMA isused to combine different input optical beams, at the same or differentwavelengths, into a higher power or multi-spectral combined focusedoutput beam to scan the scene; and

FIG. 14 is an example process flow according to aspects of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Aspects and embodiments are generally directed to active imaging systemsand methods, and, in particular, to active imaging systems and methodswhich include a Micro-Electro-Mechanical System (MEMS) Micro-mirrorArray (MMA) for active scanning applications. In certain examples, theactive imaging system includes a MEMS MMA with tip and tilt andpreferably piston micro-mirror actuation which directs and focusesillumination over a desired extent of a scene based on a detecteddirection of motion of the imaging system. Specifically, the system mayimage a leading edge of a field-of-view (FOV) of an optical receiver, ormay track one or more varying features within the FOV, based on thedetected direction of motion. Accordingly, various aspects andembodiments provide an imaging system configured to perform rapidimaging scans based on the movement of the imaging system (or variationsin motion of a feature within a scene) while maintaining a reducedweight, size, and power consumption for ground, mobile, maritime,airborne, and space imaging environments.

LCWG steering in an active imaging system provided rapid imaging scansbased on the movements of the imaging system, while maintaining areduced weight, size, and power consumption when compared to typicalimaging systems. However, LCWG steering has been found to have a numberof limitations, which may include, but are not limited to, steering avery narrow band of wavelengths about a center wavelength. Furthermoreeach material system e.g., substrates, coatings and liquid crystals, andvoltage settings to steer the laser beam are unique to each centerwavelength. Therefore to accommodate different wavelengths requiresdifferent LCWG devices and significant investment in materials,manufacturing, set-up and calibration etc. to design and field eachdevice. The LCWG cannot manipulate the wavefront of beam to, forexample, focus the beam into a spot, to provide wavefront correctione.g. atmospheric distortion, or to compensate for path lengthdifferences across the beam. The LCWG can steer one and only one beam atthe single wavelength. The LCWG cannot steer multiple beams of the sameor different wavelengths. The LCWG is limited to receive the opticalenergy from a single optical source, it cannot combine the opticalenergy from multiple sources and focus that energy into a single focusedoptical beam to provide the active illumination.

Accordingly, various aspects and embodiments discussed herein provide anactive imaging system configured to perform rapid imaging scans based onthe movements of the imaging system with the capability to manipulatethe wavefront of the beam, to segment the beam into a plurality ofindependently steerable beams of the same or different wavelengths andto combine multiple optical sources, while maintaining a reduced weight,size, and power consumption when compared to typical imaging systems.Various other advantages and benefits of the active imaging system andmethods described herein are discussed below with reference to FIGS.1-13.

FIG. 1 is a block diagram of an example active imaging system 100according to certain aspects and examples. Among other components, theactive imaging system 100 may include a positioning system 102, anoptical source 104, a Micro-Electro-Mechanical System (MEMS)Micro-Mirror Array (MMA) 106, and an optical receiver 108. Asillustrated, in certain examples the active imaging system 100 mayfurther include a Read-Out Integrated Circuit (ROIC) 110 and controlcircuitry 112. In certain examples, components of the active imagingsystem 100 may be separated into one or more subsystems, such as theillustrated scanning subsystem 114, the illustrated detection subsystem116 and the illustrated wavefront sense and correction subsystem 118.Each of the subsystems 114, 116, 118 may include various additionalcomponents in optical and/or electrical communication, as furtherdiscussed herein.

It is to be appreciated that embodiments of the methods and systemsdiscussed herein are not limited in application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the accompanying drawings. Themethods and systems are capable of implementation in other embodimentsand of being practiced or of being carried out in various ways. Examplesof specific implementations are provided herein for illustrativepurposes only and are not intended to be limiting. Also, the phraseologyand terminology used herein is for the purpose of description and shouldnot be regarded as limiting. The use herein of “including,”“comprising,” “having,” “containing,” “involving,” and variationsthereof is meant to encompass the items listed thereafter andequivalents thereof as well as additional items. References to “or” maybe construed as inclusive so that any terms described using “or” mayindicate any of a single, more than one, and all of the described terms.Any references to front and back, left and right, top and bottom, upperand lower, and vertical and horizontal are intended for convenience ofdescription, not to limit the present systems and methods or theircomponents to any one positional or spatial orientation.

Referring to the example active imaging system 100 illustrated in FIGS.1 and 2A-2B, the active imaging system 100 may include a positioningsystem 102 configured to detect a direction of motion of the imagingsystem 100 relative to a scene (e.g., scene 120). The positioning system102 may be coupled to the control circuitry 112 and one or morecomponents of the detection subsystem 116, such as the ROIC 110. Incertain examples, the positioning system 102 may include a GlobalPositioning System (GPS) configured to receive GPS positioninginformation, such as time and location data 128. The GPS system may incertain embodiments include a GPS transceiver that sends and receivesGPS positioning information with one or more GPS satellites. The GPStransceiver derives a three-dimensional position of the imaging system100 based at least in part on a plurality of GPS position signals, eachGPS signal being received from a respective GPS satellite. For instance,the GPS transceiver may convert the position derived from thepositioning information to a longitude, latitude, and height relative toan Earth-based model. Based on a series of consecutive positionmeasurements (e.g., longitude, latitude, and height), the positioningsystem 102 may determine the direction of motion of the imaging system100, relative to the scene.

While illustrated as separate from the control circuitry 112 of theactive imaging system 100, in certain examples, the positioning system102 may be combined with one or more other components of the imagingsystem 100, such as the control circuitry 112. For example, thepositioning system 102 and other combined components of the activeimaging system 100 may include a combination of software-configuredelements, control circuitry, signal processing circuitry, applicationspecific integrated circuit, or any combination of various hardware andlogic circuitry for performing the various processes discussed herein.

For example, in certain other implementations, the positioning system102 may include a Digital Signal Processor (DSP) configured to detect adirection of motion of the imaging system 100 relative to the scenebased at least in part on a variation of the scene (and/or of a featurewithin the scene) between a plurality of consecutively generated imagesof the scene. As further discussed below, in certain examples thecontrol circuitry 112 may generate one or more images of the scene basedon reflected electromagnetic radiation received from the scene at theoptical receiver 108. The DSP may compare each consecutive image toascertain one or more variations in the scene (and/or one or morevariations in at least one feature therein) between the consecutiveimages. For example, each image may be timestamped at the time ofgeneration and variations in the scene or features may include motion inone or more dimensional directions of a coordinate system relative tothe scene, such as the x-direction, y-direction, and z-directionillustrated in FIG. 1.

While discussed herein as including a GPS system and/or a DSP, incertain other examples the positioning system 102 may include any othersuitable sensing system configured to detect a direction of motion ofthe imaging system 100. Such systems may include optical sensors and/oraccelerometers, among other sensors. As further discussed below, variousother components of the active imaging system 100 may perform variousoperations based on the detected direction of motion of the imagingsystem 100.

In particular examples, the positioning system 102 may detect that thedirection of motion of the imaging system 100 relative to the scene isin any of a single-dimensional direction (e.g., x-direction), atwo-dimensional direction (e.g., x-direction and y-direction), or athree dimensional-direction (e.g., x-direction, y-direction, andz-direction) within a plane of the optical detector 108. However, incertain other examples the positioning system 102 may also detect thatthere is an absence of movement of the system 100 relative to the scene.That is, in certain examples the positioning system 102 may determinethat the imaging system 100 is stationary.

As discussed above, the positioning system 102 (e.g., the DSP) maydetermine a direction of motion of the scene based on one or morevariations in a feature within the scene. Similarly, in certain examplesthe positioning system 102 may be configured to determine a direction ofmotion of a feature within the scene, relative to the imaging system100. That is, the positioning system 102 may be configured to determinethat the imaging system 100 is stationary, while one or more featureswithin the scene (e.g., a vehicle) are moving relative to the imagingsystem 100. Similar to those processes described above, the positioningsystem 102 may identify movement of the feature within the scene, anddetermine the direction of movement of that feature based on incrementalvariations between consecutively generated images of the scene.

According to various examples, an optical source(s) 104 is in opticalcommunication a Micro-Electro-Mechanical System (MEMS) Micro-MirrorArray (MMA) 106 and configured to generate and provide a beam ofelectromagnetic radiation. In particular, the optical source 104 maygenerate the beam of electromagnetic radiation at a desired wavelength,such as any wavelength of shortwave infrared (SWIR) radiation.Accordingly, in certain examples the optical source 104 may include anactive SWIR laser configured to emit SWIR radiation within a wavelengthrange of approximately 0.9-1.7 micrometers. However, in other examplesthe optical source 104 may include any other suitable source ofelectromagnetic radiation, such as a NIR (near-infrared) laser or avisible light source.

In one embodiment, electromagnetic radiation generated by the opticalsource 104 is coherent, and the system 100 includes one or morecollimating optics. In certain embodiments, optical source 104 may emitbroadband electromagnetic radiation that spans multiple discretewavelengths. In other embodiments, different optical sources 104 mayemit electromagnetic radiation at different discrete wavelengths, whichmay either span a specified broadband or may be non-contiguous. Theoptical source may be continuous wave laser for scene illumination suchas visible, 808 nm, 980 nm or 1550 nm.

As illustrated in FIG. 1, the MEMS MMA 106 is positioned to receive thetransmitted beam of electromagnetic radiation from the optical source104. For example, the MEMS MMA 106 may receive the transmitted beam ofelectromagnetic radiation via an optical fiber or free space couplingalong a transmit path 122. Responsive to receiving the electromagneticradiation, the MEMS MMA 106 may be controlled via command signals todirect the electromagnetic radiation generated by the optical source 104through an optically transparent window 130 to form and scan an opticalbeam 132 over at least one portion of the scene. In particular, the MEMSMMA 106 may scan the electromagnetic radiation over a portion of thescene within a field-of-view of the optical receiver 116. This mayinclude directing the electromagnetic radiation over a section of thescene that is less than the entire filed-of-view of the optical receiver108, as illustrated in FIG. 1. Within FIG. 1, the field-of-view (FOV) ofthe optical receiver 108 taken at a particular instant is illustrated bythe range 124, and the scanned electromagnetic radiation is indicated bythe range 126. Over time, the optical receiver's FOV will scan a largerfield-of-regard (FOR).

In certain examples, the MEMS MMA 106 is configured to scan the receivedelectromagnetic radiation over a portion of the scene within an edgeregion of the field-of-view of the optical receiver 108. As discussedherein, each edge region may refer to one or more sections of theperimeter of the field-of-view of the optical receiver 108. Inparticular, the MEMS MMA 106 may be configured to scan the receivedelectromagnetic radiation over a portion of the scene within an edgeregion of the field-of-view that corresponds to the detected directionof motion of the imaging system 100 (e.g., a “leading” edge of thefield-of-view). For example, the control circuitry 112 may locate theportion of the scene that corresponds to the leading edge of thefield-of-view based on the direction of motion detected by thepositioning system 102. Once located, the control circuitry 112 mayoperate the MEMS MMA 106 to scan the electromagnetic radiation in anorientation substantially perpendicular to the direction of motion, atthe leading edge of the field-of-view. In various examples, the leadingedge may be intersected by a vector with an origin at the center of thefield of view in the direction of relative motion of the imaging system100.

In certain examples, the optical path length of optical beam 132 willvary across the spatial extent of the beam due to either a non-uniformthickness of optically transparent window 130, which may be flat,hemispheric, ogive or other shape, or the angle of the beam through thewindow. This induces curvature to the wavefront. The MEMS MMA 106 may beconfigured through calibration to compensate for variations in pathlength and remove the curvature.

In certain examples, it is desirable to compensate for atmosphericdistortion, which varies with time. A source 134 is positioned to emitelectromagnetic radiation e.g. SWIR in an optical beam preferably havinga “flat-top” intensity profile. Source 134 may be a pulsed laser at 1064nm. A beam steerer 136 such as a rotating mirror, LCWG or MEMS MMAsteers the beam to illuminate scene 120. A wavefront sensor 138 measuresthe wavefront of the reflected optical beam. Alternate embodiments maycombine some or all functions of the imaging and wavefront correctionsensor into a single system including the optical source, beam steeringand sensor. Control circuitry 112 generates command signals to configurethe MEMS MMA to compensate for the atmospheric distortion.

As best shown in FIGS. 2A-2B, Micro-Electro-Mechanical System (MEMS)Micro-mirror Array (MMA) 106 comprises a plurality of independently andcontinuously controllable mirrors 140 to form and steer the opticalbeam(s). Each mirror is capable of at least “Tip” (rotation about anX-axis) and “Tilt” (rotation about a Y-axis). In preferred embodiments,each mirror is also capable of “Piston” (translation along a Z-axis,perpendicular to the XY plane) where the X, Y and Z are orthogonal axesin a three-dimensional space. The Piston capability can be used toimprove the formation and scanning of the optical beam by approximatinga continuous surface across the micro-mirrors, which reduces unwanteddiffraction to increase power in the focused optical beam. The Pistoncapability can also be used to provide selective deviations from thecontinuous mirror surface to compensate for, for example, path lengthdifferences across the optical beam and atmospheric distortion. The MEMSMMA is preferably capable of steering an output laser beam over asteering range of at least −10° x+10° in tip and tilt and +/−10 microns(at least one-half wavelength in either direction) piston at a rate ofat least 1 KHz (<1 millisecond). The independently controllable mirrorscan be adaptively segmented to form any number of optical beams, adjustthe size/power of a given optical beam, generate multi-spectral opticalbeams and to combine multiple input sources. Further, the MEMS MMA musthave a sufficient number of mirrors, mirror size/resolution, fillfactor, range of motion, response time, response accuracy and uniformityacross the array. One such MEMS MMA is described in U.S. Pat. No.10,444,492 entitled “Flexure-Based, Tip-Tilt-Piston ActuationMicro-Array”, which is hereby incorporated by reference. This MEMS MMAis currently being commercialized by Bright Silicon technologies for“digitally controlling light.”

Referring to FIG. 3, illustrated is an example of electromagneticradiation received at a subset 204 of a plurality of pixels of theoptical receiver 108 of the active imaging system 100 illustrated inFIG. 1, during one mode of operation. In particular, FIG. 3 illustratesan example of the scanning operations performed by the imaging system100 while moving in a single-dimensional linear direction. Solely forthe purpose of illustration, the direction is shown in the positivey-direction in FIG. 3. During the illustrated operations, the MEMS MMA106 directs electromagnetic radiation over a portion of a scene 120(e.g., portion 202) that corresponds to an edge region of thefield-of-view of the optical receiver 108. FIG. 3 shows the MEMS MMA 106scanning the electromagnetic radiation perpendicular to the direction ofmotion of the imaging system 100 (i.e., the negative y-direction). Asillustrated, while moving in a single-dimensional direction, thedirection of motion of the scene is substantially opposite the directionof the imaging system 100. Accordingly, FIG. 3 illustrates the MEMS MMA106 scanning the electromagnetic radiation over the portion of the sceneat the leading edge of the field-of-view. While illustrated in FIG. 3 asscanning the portion immediately adjacent the leading edge of thefield-of-view, in certain examples the MEMS MMA 106 may scan a portionof the scene slightly offset from the leading edge. Moreover, in certainother examples, the MEMS MMA 106 may switch between various scanpatterns during operation and may not remain fixed on the leading edgeof the field-of-view.

Referring to FIG. 4, illustrated is an example of electromagneticradiation received at a subset 306 of a plurality of pixels of theoptical receiver 108 of the active imaging system 100 illustrated inFIG. 1 during another mode of operation. In particular, FIG. 4illustrates an example of the scanning operations performed by theimaging system 100 while moving in a two-dimensional direction. Solelyfor the purpose of illustration, the direction of motion of the scene isshown in the positive y-direction and the negative z-direction in FIG.4. During the illustrated operations, the MEMS MMA 106 scanselectromagnetic radiation over the portions (e.g., first portion 302 andsecond portion 304) of the scene 120, which correspond to a first edgeregion and a second edge region of the field-of-view, in the directionof motion for the motion in the positive y and negative z direction. Asillustrated, while moving in a two-dimensional direction, the directionof motion of the imaging system 100 is substantially opposite thedirection of the scene (i.e., the negative y-direction and the positivez-direction). In the illustrated example, the direction of motion of theimaging system 100 is diagonal relative to the scene being imaged.Accordingly, the MEMS MMA 106 illuminates the portion of the scene atthe leading edge of the field-of-view in both the negative y-directionand the positive z-direction. As illustrated, the scanned illuminationin each direction is in a substantially perpendicular orientationrelative to the detected direction of motion in the positive y andnegative z directions. While in one example, the MEMS MMA 106 maysimultaneously scan over the first portion 302 and the second portion304 (e.g., in a “L” shaped pattern), in other examples the MEMS MMA 106may rapidly scan the first portion 302 and the second portion 304sequentially.

Referring now to FIG. 5, illustrated is another example ofelectromagnetic radiation received at a subset 402 of a plurality ofpixels of the optical receiver 108 of the active imaging system 100illustrated in FIG. 1. Specifically, FIG. 5 illustrates the imagingsystem 100 during a mode of operation in which the MEMS MMA 106 scanselectromagnetic radiation over a portion of the scene 120 (e.g., portion403) which corresponds to a substantially center portion of thefield-of-view of the optical receiver 108. Solely for the purpose ofillustration, FIG. 5 shows the direction of motion of the scene in thenegative x-direction. That is, the direction of motion of the imagingsystem 100 is away from the scene being imaged. Accordingly, the MEMSMMA may illuminate the portion of the scene at the leading edge of thefield-of-view in the x-direction (illustrated in FIG. 5 as the center ofthe field-of-view).

While FIGS. 3, 4, and 5 illustrate particular examples of scanningprocesses performed by the MEMS MMA 106, in other examples, the MEMS MMA106 may perform other scanning processes and may dynamically switchbetween the modes illustrate din FIGS. 3-5 and the other scanningprocesses. These other scanning processes may provide various benefitsduring target tracking operations, such as improved accuracy, speed, andfunctionality. For instance, the MEMS MMA 106 may be configured to scanelectromagnetic radiation in a direction substantially parallel to thedetected direction of motion of the imaging system 100 (e.g.,“crabbing”). For example, the MEMS MMA 106 may scan the electromagneticradiation over a portion of the scene within the field-of-view in they-direction, while the imaging system 100 is oriented to move in they-direction, but actually moves in the z-direction for small periods oftime.

In certain other examples, the MEMS MMA 106 may be controlled todynamically track a feature within the field-of-view. In such anexample, the MEMS MMA 106 may direct the electromagnetic radiation tofollow a desired feature within the scene. For instance, the MEMS MMA106 may scan electromagnetic radiation in a direction substantiallyparallel and opposite to a detected direction of motion of the imagingsystem 100 relative to an object (e.g., a target) within the scene. Insome other examples, the MEMS MMA 106 may scan the electromagneticradiation in a direction substantially parallel and in alignment withthe detected direction of motion of the imaging system 100 relative tothe object. In still some other examples, the MEMS MMA 106 may scan theelectromagnetic radiation in alignment with, or opposite, a direction ofrotation of the imaging system 100 relative to the object within thescene. In certain other examples, the MEMS MMA 106 may be controlled tosimultaneously scan the first portion of the scene while dynamicallytracking one or more features within the field-of view. Some or all ofthese features may have been previously scanned.

As discussed in further detail below, the MEMS MMA 106 may be controlledto transmit the electromagnetic radiation in the direction of the sceneas a “fan” beam or a “spot” beam. In one example, a “fan” beam includesa beam of electromagnetic radiation having a narrow beamwidth in onedimension (e.g., a horizontal direction), and a wider beamwidth inanother dimension (e.g., a vertical direction). In contrast, a “spot”beam may include a beam of electromagnetic radiation having aconcentrated area of substantially uniform shape.

For example, the imaging system 100 may include one or more opticalelements (e.g., lens) optically coupled with the MEMS MMA 106 andpositioned so as to adjust a cross-section of the electromagneticradiation to a shape which corresponds to one or more dimensions of theoptical detector 108). For instance, a substantially rectangularcross-section may be beneficial if the scanning pattern performed by theMEMS MMA 106 is perpendicular to the direction of motion of the imagingsystem 100 relative to the scene. In certain other examples, the MEMSMMA 106 may rapidly scan electromagnetic radiation having asubstantially circular cross-section across the portion of the scene.For instance, the MEMS MMA 106 may scan the substantially circularelectromagnetic radiation over a single row or column of pixels withinthe optical detector 108 within an integration time of the detector 108.In another example, the imaging system may include a first opticalelement which converts a substantially circular cross-section to arectangular cross-section in a first dimension, and a second opticalelement which converts the substantially circular cross-section to arectangular cross-section in a second dimension. In such an example,MEMS MMA 106 may scan the electromagnetic radiation in a substantially“L” shaped pattern, as discussed above. Accordingly, various approachesmay be used to achieve a spot beam or a fan beam, as described herein.

As illustrated in FIGS. 1-5, the system 100 may include an opticalreceiver 108. The optical receiver 108 includes a plurality ofindividual detector elements, which may be referred to as pixels. Theoptical receiver 108 may include a single pixel or a line of pixels. Inone implementation the optical receiver 108 may include a Focal PlaneArray (FPA) having a plurality of pixels arranged in a series of rowsand columns. When activated to receive electromagnetic radiation, eachpixel of the optical receiver 108 is designed to collect and integratephotons of light impinging on that respective pixel. A circuitassociated with each pixel of the optical receiver accumulates chargecorresponding to the flux of incident electromagnetic radiation duringthe integration period. In one implementation, each pixel of the opticalreceiver 108 may include a complementary metal-oxide semiconductor(CMOS) sensor or a charge-coupled device (CCD). In some embodiments,charge-injection devices (CIDs) may also be used for pixels.

In various embodiments, the ROIC 110 is in optical and electricalcommunication with the optical receiver 108 (e.g., the FPA), and inparticular, each pixel of the optical receiver 108. The ROIC 110 isconfigured to activate each pixel of the optical receiver 108 during theintegration period. In particular, the ROIC 110 of various embodimentsis configured to activate pixels of the optical receiver 108 to collectreflections of the electromagnetic radiation reflected from the portionof the scene illuminated by the MEMS MMA 106. In certain examples, theMEMS MMA 106 may adjust a dwell time of the imaging system 100 tocompensate for non-uniformities and improve the performance of theoptical receiver 108.

“Row” and “column” as used herein, may be interchanged according tovarious embodiments. That is, although “row” may generally be used torefer to a horizontal positioning and “column” may generally be used torefer to a vertical positioning, as used herein either may be used torefer to a horizontal positioning and a vertical positioning relative tothe other.

In various embodiments, the MEMS MMA 106 is configured to direct opticalradiation over an area of the scene that corresponds to the activatedunit cells of the optical receiver 108. In one embodiment, the ROIC 110is configured to activate one or more unit cells of the optical receiver108 responsive to direction of the optical radiation by the MEMS MMA106. For example, the ROIC 110 may activate a subset of the plurality ofpixels of the optical receiver 108 that corresponds to the leading edgeof the field-of-view of the optical receiver 108, the trailing edge ofthe field-of-view, or any other subset of the plurality of pixels.

After the expiration of the integration period, the ROIC 110 isconfigured to deactivate each activated unit cell of the opticalreceiver 108 and read out a value for each deactivated unit cell. Eachread out value may be transmitted to other components of the imagingsystem 100 and used to construct an image of the illuminated portion ofthe scene, and/or view (e.g., track) one or more features within thescene. In particular, the control circuitry 112 may be configured togenerate a plurality of images of the scene during the operation of theimaging system 100. Each image of the scene generated by the controlcircuitry 112 may be a composition of the portion of the scene scannedby the MEMS MMA 106 and one or more images of a previously scannedportion. That is, in certain embodiments the control circuitry 112 isconfigured to “piece together” an image of the scene from various scans.In one example, the control circuitry 112 may continually refresh asection of the image based on one or more subsequent scans. For example,the control circuitry 112 may continually (e.g., automatically) refreshan area of the image that corresponds to the leading edge(s) of thefield-of-view of the optical receiver 108 or may revisit and refresh anarea of the image that corresponds to particular features of interest.

Referring again to FIG. 1, in various embodiments the imaging system 100may include control circuitry 112 coupled and in electricalcommunication with components of the active imaging system. For example,the control circuitry 112 may be in electrical communication with theROIC 110, the optical source 104, the MEMS MMA 106, and the positioningsystem 102. The control circuitry 112 may include a single controller;however, in various other embodiments the control circuitry 112 mayconsist of a plurality of controllers and/or other control circuitry.

The control circuitry 112 may include a combination ofsoftware-configured elements, signal processing circuitry, applicationspecific integrated circuitry, infrared-frequency integrated circuitry,or any combination of various hardware and logic circuitry forperforming the various processes discussed herein. For instance, thecontrol circuitry 112 of various embodiments may include a processorcore, memory, and programmable input/output components. The controlcircuitry 112 may be configured to automatically and/or dynamicallycontrol various components of the imaging system 100, such as the MEMSMMA 106.

Referring now to FIGS. 6, 7A-7B and 8, as illustrated in FIG. 6responsive to command signals from control circuitry 112 MEMS MMA 106tips and tilts all the mirrors 140 by the same angle, for example, 10degrees at an instant in time to re-direct electromagnetic radiation 600from an optical source to form and scan an optical beam 602. Asillustrated in FIGS. 7A-7B, responsive to command signals from controlcircuitry 112 MEMS MMA 106 selectively tips and tilts the mirrors 140 toform a lens to focus electromagnetic radiation 600 into optical beam602. In this example, the mirrors are tipped and tilted to implement areflective lens. The angle of the normal 604 of each mirror to theboresight 606 in the plane of the axis is the same for all mirrors ineach concentric circle of mirrors. The mirrors may be controlled toimplement a variety of optical lenses to focus the electromagneticradiation into the optical beam. As shown in FIG. 8, responsive tocommand signals from control circuitry 112 MEMS MMA 106 tips and tiltsmirrors 140 to both form a reflective lens to focus the electromagneticradiation 600 into optical beam 602 and to steer optical beam by, forexample, 10 degrees. It is important to note that the edges 610 of themirrors exhibit discontinuities. The incident electromagnetic radiation600 will diffract off of these discontinuities causing a loss of opticalpower in the focused optical beam. This problem may become morepronounced as the steering angle increases.

As illustrated in FIG. 9 responsive to command signals from controlcircuitry 112 MEMS MMA 106 tips, tilts and pistons (translates 612)mirrors 140 to approximate a continuous mirror surface 614 to both focusand scan optical beam 602. The continuous mirror surface 614approximates a single surface free-space reflective optical mirror. Eachmirror can suitably translate at least 2 wavelength and typicallyseveral wavelengths in either direction to form the continuous mirrorsurface 614. The edge discontinuities 610 and loss of power areminimized.

As illustrated in FIG. 10 responsive to command signals from controlcircuitry 112 MEMS MMA 106 can adjust the piston 612 of mirrors 140 toinduce deviations from continuous mirror surface 614. This can be doneto compensate for path length variation of the optical beam through theoptically transparent window, to correct for atmospheric distortion orboth. Adjustments for path length variation can be calibrated offlineand stored in a lookup table (LUT) as a function of scan angle.Adjustments for atmospheric distortion are done in real-time duringoperation of the active imaging system. Source 134 emits electromagneticenergy in a similar band to illumination e.g., SWIR and beam steererscans the optical beam onto scene 120. The optical beam preferably has aflat-top across the cross-section of the beam. Wavefront sensor 138measures the wavefront of the reflected beam to determine the effects ofatmospheric distortion. Control circuitry 112 computes the requisitepiston adjustments required to correct the wavefront and provides themas command signals to the MEMS MMA. In high quality, high performingactive imaging systems, the ability to accurately remove the effects ofpath length variation and atmospheric distortion is critical toachieving useful imagery of the scene, and important features identifiedwithin the scene.

As illustrated in FIGS. 11A-11D, responsive to command signals fromcontrol circuitry 112 MEMS MMA 106 is partitioned into four segments700, 702, 704 and 706 each including a plurality of mirrors 140. Thesegments do not need to be equally sized, can be any portion of thearray and can be changed on the fly in number, size or location. Inresponse to command signals, the MEMS MMA tips/tilts/pistons the mirrorsin each segment to independent form and scan optical beams 710, 712, 714and 718 over different portions of scene 120. Additional pistonactuation may be included to compensate for path length variation and/orto correct for atmospheric distortion in some or all of the opticalbeams.

As illustrated in FIG. 11B, the four optical beams 710, 712, 714 and 718are scanned in parallel over different regions 720, 722, 724 and 726 ofa leading edge region 728 of the FOV of the optical receiver. In thismanner, the first portion of the scene can be scanned in one-quarter thetime.

As illustrated in FIG. 11C, responsive to command signals from controlcircuitry 112 MEMS MMA 106 is partitioned into a plurality of segments.The mirrors in each of the segments are tipped/tilted/pistoned to formand steer at fixed angles optical beams to instantly illuminate eachpixel 730 in leading edge region 728 to instantly scan the entire firstportion of the scene. The entire scan occurs in an instant. The numberof segments and fixed optical beams may be more or less than the numberof pixels in the leading edge region.

As illustrated in FIG. 11D, responsive to command signals from controlcircuitry 112 MEMS MMA 106 directs a pair of the optical beams to scanleading edge region 728 in parallel and the other two optical beams torevisit (rescan) features 732 in a previously scanned portion of thescene. This provides the system with considerable flexibility to scanthe scene, analyze the imagery to identify features of interest and thento revisit those features to perform another or different scan withoutinterrupting the scan of the current leading edge region 728 in thedirection of motion. The MEMS MMA enables continuing the primary scanuninterrupted while investigating other features of interest.

As illustrated in FIGS. 12A-12D, responsive to command signals fromcontrol circuitry 112 MEMS MMA 106 is partitioned into four segments800, 802, 804 and 806 each including a plurality of mirrors 140. Themirrors in the different sections are provided with reflective coatings810, 812, 814 and 816 at different wavelengths. The segments do not needto be equally sized, can be any portion of the array and can be changedon the fly in number, size or location. A single broadband source may bepositioned to emit electromagnetic radiation that spans all of thewavelengths onto the entire MEMS MMA. It is more efficient to usemultiple narrowband sources 818 positioned to emit radiation at thewavelength corresponding to a respective section. In response to commandsignals, the MEMS MMA tips/tilts/pistons the mirrors in each segment toindependent form and scan optical beams 820, 822, 824 and 828 overdifferent portions of scene. Additional piston actuation may be includedto compensate for path length variation and/or to correct foratmospheric distortion in some or all of the optical beams at thedifferent wavelengths. In response to command signals, the MEMS MMA mayform and scan all of the optical beams over the first portion of thescene (the leading edge region) to provide multi-spectral illumination.Alternately, the MEMS MMA may scan one or more of the optical beams overthe first portion of the scene while scanning one or more of the opticalbeams at different wavelengths over a different portion of the scenee.g. features in previously scanned regions of the scene. In addition,one or more sections at a given wavelength may be partitioned intomultiple segments thereby generate a plurality of independently scannedoptical beams at the given wavelength.

As illustrated in FIG. 13, responsive to command signals from controlcircuitry 112 MEMS MMA 106 is partitioned into two sections 900 and 902each including a plurality of mirrors 140. Optical sources 904 and 906are positioned to emit electromagnetic radiation to illuminate themirrors in sections 900 and 902, respectively. Responsive to commandsignals the MEMS MMA tips/tilts/pistons the mirrors in sections 900 and902 to form optical beams 908 and 910, respectively. The mirrors withinin each section are further responsive to command signals totip/tilt/piston the mirrors to combine optical beams 908 and 912 into acombined optical beam 914 that is scanned over at least the firstportion of the scene. If the sources are of the same wavelength, thecombined beam behaves as if it were emitted from a single aperturelaser, but with higher power than can be obtained from a single sourceaperture. If the sources are of different wavelength, the combine beamis multi-spectral.

As described above with reference to FIGS. 1-13, several embodimentsperform processes that improve known schemes for active imaging. In someembodiments, these processes are executed by an active imaging system,such as the active imaging system 100 described above with reference toat least FIG. 1. One example of such a process is illustrated in FIG.14. According to this example, the process 500 may include the acts ofconfiguring and calibrating the MEMS MMA, detecting a direction ofmotion, emitting electromagnetic radiation from an optical source,partitioning the MEMS MMA for multi-segment and/or multi-spectraloperation, forming the optical beam(s), performing wavefront correctionfor path length variation or atmospheric distortion, scanning theelectromagnetic radiation over a portion of the scene corresponding toan edge region of a field-of-view in the direction of motion andpossibly revisiting selected portions of previously scanned scene, andreceiving reflections of the electromagnetic radiation at an opticalreceiver. The example process 500 of FIG. 5 is described with continuingreference to the imaging system 100 illustrated in at least FIG. 1.

In act 502 the process 500 may include, configuring the MEMS MMA to, forexample, provide just tip/tilt actuation or tip/tilt/piston actuation,and provide different sections of the MMA with different reflectivecoatings for independent multi-spectral operation or the same broadbandcoating to produce each optical beam with multiple spectral components.

In act 504 the process 500 may include calibrating the MEMS MMA todetermine the command signals to form or focus a particular opticalbeam, to provide specific scan angles and to compensate for path lengthvariation of the optical beam(s). For each of these the command signalsto tip/tilt/piston each mirror can be stored in different LUTs.

In act 506 the process 500 may include, detecting a direction of motionrelative to a scene to be imaged. In certain examples, detecting thedirection of motion may include detecting the direction of motion withina single-dimensional direction, while in other examples detecting thedirection of motion may include detecting the direction of motion withina two-dimensional direction. As further discussed above, eachdimensional direction (e.g., a first dimensional direction, a seconddimensional direction, etc.) may be orthogonal to the other dimensionaldirections. In certain examples, detecting the direction of motion mayinclude receiving a plurality of GPS positioning signals and determininga direction of movement of the imaging system 100 based on ascertainedcoordinates. However, in certain other examples, the process 500 mayinclude detecting the direction of motion of the imaging system 100relative to the scene based at least in part on a variation of a featurewithin the scene between one or more images of the scene. For example,the process 500 may include detecting a direction of motion of the scenebased on movement of a feature, within the scene, between consecutivelygenerated images of the scene.

In act 508, the process 500 may include emitting electromagneticradiation from the optical source(s) along the transmit path (s). Asingle narrowband or broadband optical source may illuminate the entireMEMS MMA. Multiple sources may illuminate different sections of the MEMSMMA and be combined into a single beam. Multiple narrowband sources atdifferent wavelengths may illuminate different sections of the MEMS MMAfor independent multi-spectral scanning.

In act 510, the process 500 may partition the MEMS MMA formulti-segment, multi-spectral or beam combined operation. In act 512,the mirrors within each partitioned are actuated to form the one or moreoptical beams at the same or different wavelengths.

In act 514, the MEMS MMA provides additional piston (translation)actuation of selected mirrors to perform wavefront correction on theoptical beam(s) to compensate for path length variation and/oratmospheric distortion.

In act 516, if so configured, process 500 combines optical beams frommultiple sources to increase power or form a multi-spectral beam.

In act 518, the process 500 scans an optical beam over at least a firstportion of the scene in a leading edge region in (perpendicular to) thedirection of motion. The optical beam is generally scanned perpendicularto the direction of motion to cover the leading edge region. Act 518 mayfurther include scanning additional optical beams to revisit previouslyscanned portions in act 520 or scanning additional optical beams inparallel over the first portion of the scene in act 522.

In act 524, the process 500 may include receiving, within thefield-of-view of the optical receiver 108, reflections of theelectromagnetic radiation from at least the scanned portion of the scene(e.g., the first portion and/or second portion of previously scannedregions). In particular examples, the process 500 may further includeactivating a subset of the plurality of pixels of the optical receiverto collect the reflections of the electromagnetic radiation. Inparticular examples, the subset of the plurality of pixels correspondsto the edge region(s) of the field-of-view. Specifically, activating thesubset of the plurality of pixels includes activating at least one of asingle row of pixels or a single column of pixels of the opticalreceiver 108. Such pixels may be positioned at a perimeter of theoptical receiver 108.

While not explicitly illustrated or described with reference to FIG. 5for the convenience of description, the example process 500 illustratedtherein may include further acts and processes. Examples of theseadditional acts and processes are described with reference to theexample active imaging system 100 illustrated in FIGS. 1-13.

Accordingly, various aspects and embodiments discussed herein provide anactive imaging system configured to perform rapid imaging scans based onthe real-time movements of the imaging system, while also maintaining areduced weight, size, and power consumption. Specifically, certainexamples may scan a leading edge, a trailing edge, or other desiredsections of a scene that are less than an entire field-of-view of thereceiver. Such examples offer the benefit of improved imagingefficiency, in addition allowing the recapture of missed image data,recapture of image data from desired sections of the scene, and dynamictracking of features within the scene. Such features are particularlybeneficial when the imaging system (and/or features within the scene) isin motion.

Having described above several aspects of at least one embodiment, it isto be appreciated various alterations, modifications, and improvementswill readily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be part of thisdisclosure and are intended to be within the scope of the invention.Accordingly, the foregoing description and drawings are by way ofexample only, and the scope of the invention should be determined fromproper construction of the appended claims, and their equivalents.

We claim:
 1. An active imaging system comprising: a positioning systemconfigured to detect a direction of motion of the imaging systemrelative to a scene to be imaged; at least one optical source positionedto emit electromagnetic radiation along a transmit path; aMicro-Electro-Mechanical System (MEMS) Micro-Mirror Array (MMA)comprising a plurality of independently and continuously controllablemirrors to tip and tilt each mirror about first and second orthogonalaxes, said MEMS MMA positioned along the transmit path to receive theelectromagnetic radiation from the at least one optical source andresponsive to command signals to tip and tilt the mirrors to form andscan the electromagnetic radiation in an optical beam over at least afirst portion of the scene within a field-of-view of an opticalreceiver; and the optical receiver positioned to receive reflections ofthe electromagnetic radiation from at least the first portion of thescene within the field-of-view, wherein the first portion of the sceneis within a first edge region of the field-of-view of the opticalreceiver, the first edge region being in the direction of motion of theimaging system.
 2. The active imaging system of claim 1, wherein saidmirrors are configured to translate in a third axis orthogonal to aplane containing the first and second orthogonal axes to form and scanthe beam.
 3. The active imaging system of claim 2, wherein mirrors areresponsive to command signals to translate along the third axis to focusand scan the optical beam.
 4. The active imaging system of claim 3,wherein the mirrors are responsive to command signals to tip, tilt andtranslate to approximate a continuous mirror surface to focus and scanthe optical beam.
 5. The active imaging system of claim 3, furthercomprising an optically transparent window, wherein responsive tocommand signals the MEMS MMA translates the mirrors to producedeviations from the continuous mirror surface to compensate for pathlength variation of the optical beam through the optically transparentwindow.
 6. The active imaging system of claim 3, further comprising aseparate optical source positioned to emit electromagnetic radiationhaving a flat-top intensity profile and a wavefront sensor to measure awavefront of the reflected electromagnetic radiation off of the scene,wherein responsive to the measured wavefront and command signals theMEMS MMA translates the mirrors to produce deviations from thecontinuous mirror surface to provide wavefront correction for theoptical beam to compensate for atmospheric distortion.
 7. The activeimaging system of claim 1, wherein responsive to command signals theMEMS MMA partitions the mirrors into a plurality of segments, eachsegment comprising a plurality of mirrors responsive to command signalsto tip and tilt the mirrors to form and independently scan theelectromagnetic radiation into a laser beam.
 8. The active imagingsystem of claim 7, wherein the MEMS MMA is responsive to command signalsto scan the plurality of laser beams in parallel over differentsub-portions of the first portion of the scene.
 9. The active imagingsystem of claim 7, wherein the MEMS MMA is responsive to command signalsto fix the plurality of laser beams to instantly illuminate the entirefirst portion of the scene.
 10. The active imaging system of claim 7,wherein the MEMS MMA is responsive to command signals to scan at leastone of the plurality of laser beams over the first portion of the sceneand to scan at least one of the plurality of focused laser beams torevisit a previously scanned portion of the scene.
 11. The activeimaging system of claim 1, wherein the optical source emitselectromagnetic radiation over a broadband that includes multiplediscrete wavelengths, wherein the mirrors are provided with a reflectivecoating that reflect over a band that includes the multiple discretewavelengths, whereby the optical beam comprises the multiple discretewavelengths to scan the first portion of the scene.
 12. The activeimaging system of claim 1, wherein responsive to command signals theMEMS MMA partitions the mirrors into a plurality of sections eachcomprising a plurality of mirrors, wherein the mirrors in the differentsections comprise reflective coatings designed to reflect at differentwavelengths within the specified band, wherein within each section themirrors are responsive to command signals to tip and tilt the mirrors toform the electromagnetic radiation into a optical beam at thecorresponding wavelength.
 13. The active imaging system of claim 11,wherein responsive to command signals at least one section of the MEMSMMA is partitioned into a plurality of segments each segment comprisinga plurality of mirrors, wherein within each segment the mirrors areresponsive to command signals to tip and the mirrors to form theelectromagnetic radiation into an optical beam at the wavelength of thecorresponding section.
 14. The active imaging system of claim 11,wherein responsive to command signals the MEMS MMA scans the pluralityof optical beams at the different wavelengths over the first portion ofthe scene.
 15. The active imaging system of claim 11, wherein responsiveto command signals the MEMS MMA scans at least one optical beam over thefirst portion of the scene and another optical beam at a differentwavelength over a different portion of the scene.
 16. The active imagingsystem of claim 1, wherein responsive to command signals the MEMS MMApartitions the mirrors into sections each section comprising a pluralityof mirrors, further comprising a plurality of optical sources positionedto emit electromagnetic radiation along different transmit paths toilluminate different sections of the MEMS MMA, each said sectionresponsive to command signals to tip and tilt the mirrors to focus theelectromagnetic radiation in an optical beam, each said section furtherresponsive to command signals to tip and tilt the mirrors to combine theplurality of optical beams into a combined optical beam that is scannedover at least the first portion of the scene.
 17. An active imagingsystem comprising: a positioning system configured to detect a directionof motion of the imaging system relative to a scene to be imaged; atleast one optical source positioned to emit electromagnetic radiationalong a transmit path; a Micro-Electro-Mechanical System (MEMS)Micro-Mirror Array (MMA) comprising a plurality of independently andcontinuously controllable mirrors to tip and tilt each mirror aboutfirst and second orthogonal axes, and translate in a third axisorthogonal to a plane containing the first and second orthogonal axes toform the beam, said MEMS MMA positioned along the transmit path toreceive the electromagnetic radiation from the at least one opticalsource and responsive to command signals to partition the MMA into aplurality of segments, each segment comprising a plurality of mirrors totip, tilt and translate the mirrors to approximate a continuous mirrorsurface to focus and independently scan the electromagnetic radiation inan optical beam over at least a first portion of the scene within afield-of-view of an optical receiver; and the optical receiverpositioned to receive reflections of the electromagnetic radiation fromat least the first portion of the scene within the field-of-view,wherein the first portion of the scene is within a first edge region ofthe field-of-view of the optical receiver, the first edge region beingin the direction of motion of the imaging system.
 18. The active imagingsystem of claim 17, wherein the mirrors in the different segmentscomprise reflective coatings designed to reflect at differentwavelengths within the specified band, wherein within each segments theMEMS MMA mirrors are responsive to command signals to tip, tilt andtranslate the mirrors to form the electromagnetic radiation into afocused optical beam at the corresponding wavelength.
 19. The activeimaging system of claim 17, further comprising: an optically transparentwindow through which the optical beam passes: a separate optical sourcepositioned to emit electromagnetic radiation having a flat-top intensityprofile through the optically transparent window; and a wavefront sensorto measure a wavefront of the reflected electromagnetic radiation off ofthe scene and passing back through the optically transparent window,wherein responsive to command signals the MEMS MMA translates themirrors to produce deviations from the continuous mirror surface toprovide compensation for path length differences of the optical throughthe window and wavefront correction for the optical beam to compensatefor atmospheric distortion.
 20. An active imaging system comprising: apositioning system configured to detect a direction of motion of theimaging system relative to a scene to be imaged; a plurality of opticalsources positioned to emit electromagnetic radiation along differenttransmit paths; a Micro-Electro-Mechanical System (MEMS) Micro-MirrorArray (MMA) comprising a plurality of independently and continuouslycontrollable mirrors to tip and tilt each mirror about first and secondorthogonal axes, and translate in a third axis orthogonal to a planecontaining the first and second orthogonal axes to form the beam, saidMEMS MMA partitioned into a plurality of sections positioned along thetransmit path to receive the electromagnetic radiation from theplurality of optical sources in the respective sections, each sectioncomprising a plurality of mirrors responsive to command signals to tip,tilt and translate the mirrors to approximate a continuous mirrorsurface to focus the electromagnetic radiation in an optical beam, eachsection further responsive to command signals to combine the pluralityof focused optical beams into a combined focused optical beam to scan atleast a first portion of the scene within a field-of-view of an opticalreceiver; and the optical receiver positioned to receive reflections ofthe electromagnetic radiation from at least the first portion of thescene within the field-of-view, wherein the first portion of the sceneis within a first edge region of the field-of-view of the opticalreceiver, the first edge region being in the direction of motion of theimaging system.
 21. The active imaging system of claim 20, furthercomprising: an optically transparent window through which the opticalbeam passes: a separate optical source positioned to emitelectromagnetic radiation having a flat-top intensity profile throughthe optically transparent window; and a wavefront sensor to measure awavefront of the reflected electromagnetic radiation off of the sceneand passing back through the optically transparent window, whereinresponsive to command signals the MEMS MMA translates the mirrors toproduce deviations from the continuous mirror surface to providecompensation for path length differences of the optical through thewindow and wavefront correction for the optical beam to compensate foratmospheric distortion.